Binaural loudness summation is known in the field of audiology. Binaural loudness summation is the effect that the loudness of sound is greater when it is presented to both ears simultaneously than when it is presented to one ear alone. The magnitude of this effect varies between individuals. Usually, the increase in loudness is approximately 3 dB when the intensity level is near the person's hearing threshold. The effect increases at suprathreshold level.
Binaural loudness summation is one of the advantages of binaural amplification. For persons with bilateral hearing loss who are equipped with two hearing instruments, the applied gain may be reduced. Due to the reduced gain, the chance of feedback is decreased, and larger vents may be used.
Since the optimal gain is different between monaural and binaural fittings, the loss of binaural loudness summation accounts for a non-ideal gain fitting if a user, who usually wears two hearing instruments, occasionally only uses one hearing instrument. This may happen if the user deliberately only wears one hearing instrument or if one of the hearing instruments is not available.